Monday, 25 January 2021
88 per cent of potato fields tested in England and 94 per cent Scotland have been found to have Root lesion nematodes (RLN) populations, a survey by PhD student Valeria Orlando has found.
Using qPCR molecular identification method, 200 fields from England were surveyed in counties with the highest potato production, plus 17 samples from Scotland. Extra information about the fields was provided from a questionnaire completed by growers.
Valeria explained: “We were looking to discover not only the presence of RLN, but also to identify the species and their population proportion.”
Populations were identified of Pratylenchus crenatus, P. neglectus, P. penetrans and P. thornei.
“Overall, we found that RLN are widely present in England with significantly higher prevalence in the East and North East of England.
“When we looked at the numbers of the individual species, we learned that P. neglectus was the most abundant of the species found mainly in East of England, with 31 per cent of the share of the total.”
Looking at her results in more detail, Valeria pointed out interesting regional differences; P. crenatus were found in the East and West of England, but were less abundant than other species while P. penetrans was found in the East and South East of England.
P thornei had occurred only in the South East and South West, with no populations of this species being detected further north.
Other minor species were more widespread across England, she said.
The 17 samples taken in Scotland showed 94 percent detected high presence, the main species were P. neglectus and P. crenatus.
“It was interesting to find that on the whole, mixtures of species were found together in the same sample,” she noted.
Moving on to give details of how the experiments had been done, she revealed that the soil surveys were done between September and November, using a W pattern grid over 1ha of the field with 60 cores per kg of soil and at a depth of 20 cm.
Details were collected about soil type, the last crop grown before sampling, noting whether it was post-harvest potato (48 per cent), potato (27 per cent), fallow, or cereals. Information was also recorded about the previous crop in the rotation, and Valeria reported that 50 per cent of the time it had been wheat. Further data was collected on whether a nematicide had been used, and if so, which one.
“We also looked at the history of potato cyst nematodes (PCN) in these fields, and found that 45 percent of them were known to occur in the field, while 40 per cent were reported to have an absence of them. The was no information on the remaining 20 per cent of fields.”
“We took care to ensure our molecular method of identifying species and population numbers were viable, so we compared this new method with traditional counting by microscopy, and molecular identification was found to be sensitive, fast and accurate,” she said.
Current practices for reduction of initial nematode population densities and minimising reproduction during the growing season are done by a combination of different methods, such as: nematicides, crop rotation, cover crops with Tagetes spp, and biofumigation. These have different levels of effectiveness according to the species of RLN, for example biofumigation tends to be more effective on P. neglectus than P. penetrans, she noted.
“RLN are involved in root disease complexes with Rhizoctonia solani, Pythium spp. and Verticillium dahliae.
“Damage thresholds for P. penetrans on potatoes are 1-2 nematodes/g soil although this may change among different species, soil types and cultivars.”
“Only 10 percent of the farmers in the survey had tested the soil for root lesion nematodes, which highlights that the presence of this nematode is not yet well known.”
Root lesion nematodes
The most common species of root lesion nematode (RLN) in potato crops are Pratylenchus penetrans, P. crenatus, P. neglectus, P. alleni, P. thornei and P. scribneri.
When present, they can affect roots, haulm and tubers, making dark coloured necrotic lesions and causing poor root and haulm development, and resulting in stunted plants. When there are high populations in the soil they can create wart-like protuberances or a scabby appearance on the tubers.